‘Precision seismology’ encompasses a set of methods which use differential measurements of time-delays to estimate the relative locations of earthquakes and explosions. Delay-times estimated from signal correlations often allow far more accurate estimates of one event location relative to another than is possible using classical hypocentre determination techniques. Many different algorithms and software implementations have been developed and different assumptions and procedures can often result in significant variability between different relative event location estimates. We present a Ground Truth (GT) dataset of 55 military surface explosions in northern Finland in 2007 that all took place within 300 m of each other. The explosions were recorded with a high signal-to-noise ratio to distances of about 2°, and the exceptional waveform similarity between the signals from the different explosions allows for accurate correlation-based time-delay measurements. With exact coordinates for the explosions, we are able to assess the fidelity of relative location estimates made using any location algorithm or implementation. Applying double-difference calculations using two different 1-D velocity models for the region results in hypocentre-to-hypocentre distances which are too short and it is clear that the wavefield leaving the source region is more complicated than predicted by the models. Using the GT event coordinates, we are able to measure the slowness vectors associated with each outgoing ray from the source region. We demonstrate that, had such corrections been available, a significant improvement in the relative location estimates would have resulted. In practice we would of course need to solve for event hypocentres and slowness corrections simultaneously, and significant work will be needed to upgrade relative location algorithms to accommodate uncertainty in the form of the outgoing wavefield. We present this data set, together with GT coordinates, raw waveforms for all events on six regional stations, and tables of time-delay measurements, as a reference benchmark by which relative location algorithms and software can be evaluated.

中文翻译：

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地震事件相对位置的基准案例研究

“精密地震学”涵盖了一组方法，这些方法使用时间延迟的差分测量来估计地震和爆炸的相对位置。从信号相关性估计的延迟时间通常可以比使用传统的偏心确定技术更准确地估计一个事件相对于另一个事件的位置。已经开发出许多不同的算法和软件实现方式，并且不同的假设和过程通常可以导致不同的相对事件位置估计之间的显着差异。我们展示了2007年芬兰北部发生的55次军事地面爆炸的地面真相（GT）数据集，这些爆炸都发生在彼此之间300 m之内。爆炸以高信噪比记录到大约2°的距离，而且来自不同爆炸的信号之间异常的波形相似性允许进行基于相关的准确时间延迟测量。有了爆炸的精确坐标，我们就能评估使用任何定位算法或实现方法做出的相对位置估计的保真度。使用两个不同的一维速度模型对该区域应用双差计算会导致距中心的距次中心距离太短，并且很明显，离开源区域的波场比模型所预测的更为复杂。使用GT事件坐标，我们能够测量与从源区域发出的每个射线相关的慢度矢量。我们证明，如果可以进行此类更正，相对位置估计值将得到显着改善。在实践中，我们当然需要同时解决事件震源和速度校正问题，并且需要大量工作来升级相对定位算法，以适应输出波场形式的不确定性。我们提供此数据集以及GT坐标，六个区域站上所有事件的原始波形以及时延测量表，以作为参考基准，通过该基准可以评估相对定位算法和软件。